Envelop.



ROBERT D. TOWNSEND, OF CHICAGO, ILLINOIS.

ENVELOP.

Specification of Letters Patent.

Patented July 20, 1909.

Application filed January 15, 1908. Serial No. 410,923.

To all whom it may concern:

Be it known that l, ROBERT D. TowNsnND, citizen of the United States, residing at Chicago, in the county of Cook and State of lllinois, have invented a certain new and useful improvement in Envelope, of which the following is a full, clear, concise, and exact det r coloring matter or dye 1s used and moisture scription, reference being had to the accompanying drawings, forming a part of this specification.

My invention relates to envelops, it-s object being to produce an envelop provided with indicating means for indicating whether or not the envelop has been tampered with or opened before reaching the person to whom it is addressed.

ln accordance with my invention l run a thread or threads through the gummed area of the flap and this thread may be treated with wax, coloring matter, chemicals, or any other composition which upon being subjected to moisture or heat beyond a certain degree will change its condition to cause indication of the fact that heat or moisture has been applied, and so give evidence that the envelop has been tampered with and either opened or attempt made to do so.

ln the accompanying drawing my invention is plainly illustrated, Figure l being a rear of a closed envelop showing the detecting means applied, Fig. 2 is a similar view showing the envelop tlap opened, F ig. 3 is an enlarged sectional view showing one disposition of a single thread, while Fig. 4 is an enlarged sectional view showing the location of two threads applied by an ordinary sewing machine.

0n the flap l of an ordinary envelop, the section 2 along the edge is gummed. When the envelop is to be closed, this gummed area is irst moistened and then the flap pressed into engagement with the envelop body. The usual method for unlawfully opening the envelop is to subject it to heat or moisture, usually by applying steam thereto, which has the effect of softening the gum to allow opening of the flap. Sufficient gum will remain to again close the envelop, or additional gum may be applied, and this work can be so neatly and skilfully done that it is impossible to detect whether or not the" envelop has been tampered with. I, however, run a thread or threads bach and forth through the gummed section of the flap, and preferably treat the thread with some composition such as a soluble dye or waX, whose condition will change when subjected to heat or moisture so that indication will be given that attempt has been made to open the envelop. lf wax is used and heat applied, the wax will flow into and spread along the paper of the envelop, and if the wax is colored a very plain indication will be given. When applied, the dye or coloring matter will soak into the paper and discolor it and thereby give plain indication.

The thread may be applied in various ways. F or example, as shown in Fig. 3, a single thread 3 may be applied with an ordinary running stitch, part of the thread then being on the inside of the flap and the thread having been previously treated with the proper material. The thread may be applied either before or after the gum has been applied', and it is perhaps better to 'apply it before, as in this case the gum will serve to hold the thread in position and will also form a protective coating over the inner thread sections so that when moisture is applied preparatory to sealing the envelop, the thread will not be sufficiently moistened to cause running of the coloring matter. The best and cheapest arrangement, however, is to apply two threads by means of ordinary sewing machines, this arrangement being shown in Fig. 4. lf the flap is sewed from the top, then the outer thread l will loop through the successive needle openings 5 and the inner thread 6 will be shuttled through these loops; while if the flap is sewed from the under side, the loop thread will be on the inside of the iiap and the straight thread on the outside. By thus sewing in the threads they are securely locked in position. Another advantage with this arrangement is that only the outside thread need be treated, and with this ar rangement considerable moisture may be applied to the gummed surface and the inner thread before su'lhcient moisture will pass through the stitch openings 5 to cause the running of the coloring matter or other ma terial with which the outer thread is treated. ln this arrangement, also, the gum may be applied either before or after the sewing of the threads.

rlhe application of the threads need not be continuous, but may be in sections, or any other arrangement thereof may be used. A monogram or seal design may be sewed on the liap in any position, and the threads may also be applied in positions otherwise than in the gummed areas.

The envelop of my invention can be manufactured very cheaply as the threads can be very quickly and efficiently applied by machinery.

Having thus described my invention, I desire to secure the following claims by Letters Patent:

l. In an envelop, the combination with an envelop body of a normally open flap, sealing gum applied to the under side of the edge of the flap, and a thread sewn back and forth through the gummed area of the flap, the said thread coming in contact with the gumrned surface on one side of the flap and into contact with the ungummed surface on the other side of the flap, the said thread being treated with a substance adapted to mark the material of which the flap and envelop body are made upon the application of moisture and heat thereto.

2. In an envelop, the combination with a paper' envelop body of a normally open flap of the same material, sealing gum applied to the under side of the edge of the flap, and a thread impregnated with a soluble dye-stuff sewn back and forth through the gummed area of the flap, said thread coming into contact with the gummed surface on one side of the fla p and into contact with the ungummed surface on the other side of the flap, whereby the application of moisture to the gummed area of the flap will dissolve the dye-stuff and cause it to mark the flap or envelop body.

3. In an envelop, the combination with a sealing flap, of an adhesive gum applied to the inner surface of said flap near its edge, a thread sewn through said gunnned portion, said thread occupying a position partly on the gnmmed surface of said Hap and partly on the nngummed surface, and a soluble dye stuff impregnated in said thread said dye stuff adapted to dissolve and stain said envelop on the application of heat or moisture.

In witness whereof, I hereunto subscribe my name this 13th day of January A. D.,

ROBERT D. TOVNSEND. Vitnesses CHARLES J. SCHMIDT, GEORGE E. HIGHAM. 

